GPS Icon always on?

Does the GPS icon stay on all the time if you have GPS turned on? Or does it only stay on when an app is using it?

If it only stays on when an app is using it, how can I find out what particular app is using the GPS, and then close it.

Finally, if it only stays on when an app is using it, and it does shut off, does that mean the GPS is no longer active, and will only become active when an app is using it again?

EDIT: Never mind. I figured it out. The icon does indeed shut off if an app isn't using it. Was testing Mobile Defense. Accuracy of 3200 feet due to being in a concrete building and not being able to acquire a GPS signal, but it's certainly trying lol